The combination of the recent increase in Personal Media Players (PMPs) and rises in urban noise levels have all contributed to the ubiquity of in-ear-canal (or insert) earphones. Such insert headphones afford the user of 20-35 dB of passive noise attenuation, thereby allowing an increase signal-to-noise ratio for reproduced Audio Content (e.g. music from a PMP). This is advantageous for loud-noise work environments; such as medical operating rooms where sound pressure levels can reach in excess of 120 dB (Kracht et al, 2006). The assembly housing the earphones in the left and right ear of the user is, furthermore, ideally situated to house a number of microphones to facilitate binaural recording of the user's sound exposure.
U.S. Pat. No. 6,728,385 describes a system that uses the assembly described in U.S. Pat. No. 7,039,195 to detect user-created voice by comparing the signal level of the ECM and ASM's in one earphone device to operate a VOX automatic “push-to-talk” switch. U.S. Pat. No. 7,039,195 also describes for in-situ estimation of the overview attenuation provided by the earpiece (i.e. a NRR).
U.S. Pat. No. 6,661,901 describes a system that uses the assembly described in U.S. Pat. No. 7,039,195 and a signal processing circuitry to transform the ECM signal into a signal which sounds natural to the user after processing and auditioning with the ECR.
A fall monitoring device is described in U.S. Pat. No. 6,433,690 comprising an accelerometer to detect whether the user's body is at an angle indicative of a fall. U.S. Pat. No. 6,647,368 also describes a method for detecting changes in head location using a pair of microphones to detect air pressure changes within and external to an occluded ear canal.